English singer-songwriter Ellie Goulding performs at the Fillmore Silver Spring on Jan. 20. (Kyle Gustafson/For The Washington Post)

She’s a little bit pop, she’s a little bit electro and sometimes she whips out a guitar. So how exactly do you categorize British sensation Ellie Goulding? The answer to that question came Sunday night at a sold-out Fillmore, and it was a resounding “you don’t.” Her set played like a bumping dance party with some “MTV Unplugged”-style interludes, and, in a logic-defying twist, it worked.

Over the past few years, Goulding has cobbled together a diverse fan base on the strength of her kinda-electronic, kinda-indie, kinda-infectious smash single “Lights.” Thanks to “Lights,” the small-town girl from England has become the rare crossover act that unassuming mainstream consumers can enjoy without getting scoffed at by their more “discerning” friends. In October, Goulding released her second album, “Halcyon,” a dance-heavy trip through the darker, wilder places in the post-breakup psyche that features jarring, sputtering, often downright unpretty sounds juxtaposed with songbird vocals.

From her first moments onstage Sunday night, Goulding made it clear that her expectation-eschewing antics weren’t just for the studio. Eyes closed, she unceremoniously interrupted her own welcoming cheer with a high, otherworldly whimper to introduce “Don’t Say a Word.”

Yep — the pale, soft-spoken, 26-year-old would be doing pretty much whatever she felt like doing this evening. The rest of us were just there to watch it happen.

Throughout much of the first half of her set, it was easy to imagine that it might have looked and sounded exactly the same without the audience there. Dressed in a gray T-shirt, black leather shorts and boots, Goulding declined to interact much with her fans; rather, she hit her crystalline high notes while wandering from one side of the stage to the other, pausing frequently to pitch forward, shoulders first, as she cleared some of her more athletic vocal hurdles.

There was a shift when Goulding sent most of her band offstage for an elegant, pianist-accompanied rendition of Elton John’s “Your Song,” which she performed in 2011 at the wedding ceremony of the Duke and Duchess of Cambridge. (In Britain, she’s better known as a fluttery-voiced folk-pop pixie than an electro icon.) When an auditorium full of undergrad, Urban Outfitters types began to belt along, Goulding seemed to finally notice that an audience had gathered. Only then did it start to feel more like a show and less like a recital.

“I’m usually really shy between songs,” she conceded at one point before launching into a giggly anecdote about her brother and his death metal band. Was it intelligible? Not really, but it was certainly adorable.

By the time “Lights” came around, Goulding was once again doing her own thing — spreading her arms like airplane wings and sometimes simply whipping her hair around with her back to the crowd. She was in a good place, and for the rest of us, it was a joy just to be invited along.

Fetters is a freelance writer.